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The Mystery of Blindsight Helps Us Understand the Mind Better

Michael Egnor
Photo credit: Ryoji Iwata via Unsplash.

Blindsight is the remarkable ability of some blind people to sense objects that they cannot actually see. It occurs when the blindness is caused by damage to the main part of the brain that processes visual information (the striate cortex). But the eyes themselves are intact. The eyes continue to see (sensation) but nothing is receiving the messages (perception). Or so we would think, except for this:

One of the most contentious discussions in philosophy of mind and neuroscience is the nature of perception as opposed to sensation. How can we perceive objects in our environment? On a deeper level, what do we mean by “perception”? In what ways does perception differ from sensation, if at all?

How Classical Scholastic Philosophy Helps

The neurobiology of perception provides an excellent example of the ways in which classical scholastic philosophy can help us understand the mind. Our modern materialistic and mechanistic theories of the mind often confuse us. They detract from understanding rather than contributing to it.

From the classical perspective, sensation is the reception of the form of an external object on the sensory organ. In the case of sight, sensation is the activation of the retina caused by light entering the eye. Perception is the interpretation of that sensation. It should be noted that, while the eye and the brain are the organs by which sensation and perception respectively are accomplished, the person using the sensory and perceptual powers of the soul* is the agent who is sensing and perceiving.

From the modern perspective, which is generally a mechanistic understanding of neurobiology, sensation entails a series of biochemical reactions in the retina and the optic apparatus and perception involves interpretation carried out by the cerebral cortex. From this perspective it is assumed that the cerebral cortical is needed for any level of awareness of objects in the visual field.

A classical challenge to that mechanistic view is blindsight. A person who has lost the striate cortex, which is a portion of the occipital lobe that represents the primary area where visual information is processed, cannot see in the normal sense. But, paradoxically, cortically blind people can often demonstrate awareness of objects in their visual field even though they say that they cannot see the object.

For example, as in the video above, a blind person who has blindsight will walk straight down a hallway, unable to see what is in front of him. However if there is an obstacle placed in front of him, he will go around the obstacle. If asked why he went around the obstacle he will say that that just seemed to be the right path to take. But he would deny that he saw an obstacle that caused him to take that path. Thus blindsight appears to be a level of awareness that does not involve consciousness or identification of a specific object in the visual field.

A Problem for Understanding Blindsight

Modern mechanistic understandings of the mind/brain relationship clearly present a problem for understanding blindsight. How can a person have awareness of an object in his visual field without being conscious of it? What could the neurobiological basis of this unusual situation be? Most theories of blindsight invoke intermediate connections between the eyes and the visual cortex that go to other parts of the brain. These connections are thought to permit a kind of preconscious awareness of objects in the visual field (as asserted in the video). But the neurobiology on which that explanation depends is unclear and not at all well understood.

Read the rest at Mind Matters News, published by Discovery Institute’s Walter Bradley Center for Natural and Artificial Intelligence.